The invention relates to a wireless communication network system for exchanging data packets between computers, and between computers and peripheral equipments such as printers, digitizing tablets, keyboards, and pointing devices or mice, within a small local area such as an office or closely arranged group of offices.
Wireless communication networks may vary from one using a point-to-point type system where one node speaks only to one other node as in a peer-to-peer or host-to-host system, or a point and shoot type system that operates much like a television remote control in communicating with other nodes, to a true multinode system continually requiring multiple communication paths. U.S. Pat. Nos. 4,232,299; 4,775,928; 4,992,787, 5,075,792; 5,204,768; and 5,307,297 are representative.
All wireless communication networks can be conveniently classified in accordance with the area they cover. A network that covers an area having a cross-distance of miles is generally referred to as a metropolitan area network (MAN) or wide area network (WAN). A wireless network that covers cross-distances of the order of hundreds of feet generally is referred to as a local area network (LAN). Each of the above networks employ complex and costly communication protocols, which in turn require expensive hardware for implementation in accommodating information exchanges between multiple nodes. These prior implementations are impractical for use with a small area network covering, by way of example, an office where wireless communication with a computer or peripheral equipment may be desired. U.S. Pat. Nos. 4,665,519 and 5,241,542 are representative.
In a wireless network, access contention is a major concern. In general, a multiple access method can be described as either circuit switched or packet switched. Circuit switched networks are those where a connection must be continuously maintained, as with a telephone. As a result, the number of users is strictly limited. A packet switched network allocates capacity to users as a slice of time, but the connection between users only lasts for the duration of the packet. During the transmission of the packet, however, the entire capacity of the channel is available to the transmitting node. This transient connection of a packet switched network is ideal for situations where a relatively large number of nodes need to make infrequent connections to each other to communicate by rapid bursts of information.
A number of access control schemes have been developed including time division multiple access (TDMA), frequency division multiple access (FDMA), code division multiple access (CDMA), and carrier sense multiple access (CSMA). A description of the CSMA scheme may be found in xe2x80x9cWireless LAN Systemsxe2x80x9d, by A. Santamaria and F. J. Lopez-Hernandez, pages 210-212, Artech House, 1994.
The TDMA, FDMA and CDMA control schemes have been successfully used with networks where continuous data streams are issued by a small number of nodes. Where data packets are issued rapidly from a large number of nodes, however, the CSMA control scheme has been favored. In wireless systems where relatively short bursts of data or data packets are transmitted at high speeds, the CSMA control scheme is ideal. U.S. Pat. Nos. 4,665,519 and 5,241,542 are representative.
When a network is comprised of a large number of nodes, there must in addition be a means for preventing two or more users from attempting to use a network channel simultaneously. In a wired system, a Collision Detection system usually is used in which a node compares a signal traveling over a wire with a signal that it is attempting to send. No signal is transmitted by the node as long as the compared signals differ, or until no signals are detected in the transmission channel. In a wireless system, where a network node has both a transmitter and a receiver means, and the receiver means stays energized until such time as a transmission of information is required, the occurrence of activity in a transmission channel can be detected. As with the wired communications system, the transmission can be delayed until no activity in the transmission channel is detected. The potential still exists for two or more network nodes to begin a data packet transmission at approximately the same time. A receiver in such an event will likely receive a corrupted packet and not acknowledge a successful transmission. For this reason, Collision Avoidance is used, wherein a transmitter waits or pauses before retransmitting if no acknowledgement is received within a specified time period after a first transmission. The transmission wait time is referred to as the backoff period. In known complex network protocols, the backoff period is chosen randomly according to a statistical rule.
The combination of CSMA and Collision Avoidance is referred to as CSMA/CA multiple access control. Wireless systems have been made that include CSMA/CA capabilities implemented with a MAN, WAN or LAN protocol. Such complex and expensive systems are not practical for a small area network such as a Desktop Area Network (DAN), where communication is desired with a computer or peripheral device, between computers, or between a computer and a peripheral device located in an office or in adjacent offices. While U.S. Pat. No. 4,665,519 may be said to be representative, it is a low performance, narrow band system which requires a complex and costly conversion of an RS-232C serial interface into an HDLC multipoint protocol through use of manually set DIP switches. Further, the patent discloses the use of random backoffs and manually switched frequencies, and thus is not a true CSMA system.
The invention is a wireless, high performance, broadband Desktop Area Network (DAN) system, which includes CSMA CA multiple access control with Collision Avoidance that is implemented by utilizing a serial bus data packet protocol to accommodate wireless communication among multiple nodes. Synchronized data packet exchanges are accommodated with the between computers, between computers and peripheral equipments, and with peripheral equipments including but not limited to keyboards, printers, facsimilie machines, digitizing tablets, and pointers or mice.
In one aspect of the invention, a timing recovery method is used which is based upon a data packet structure that includes a preamble with an alternating data stream from which timing information may be extracted to synchronize the processing of the data packet.
In another aspect of the invention, CSMA multiple access control is implemented by utilizing a serial bus data packet protocol to accommodate wireless exchanges of data packet information not only between a computer and peripheral equipment, but also between computers (peer to peer).
In still another aspect of the invention, interference between nodes in transmitting messages is controlled through use of both a delay method which causes a transmitting node to wait until a communication channel is idle before transmitting data packet information, and a Collision Avoidance method in which all transmitting nodes upon failing to receive an acknowledgement signal from a target receiving node will wait for a period of time (proportional to the transmitting node""s network address) before attempting to retransmit the message.
In a further aspect of the invention, the CSMA CA multiple access control and timing recovery methods are not hardware dependent on the type of interface used to transmit and receive data packets.
In a still further aspect of the invention, only the controller need by reconfigured for host to host portability of a node subsystem comprising a controller, a transmitter, a receiver and an interface for receiving and sending modulated information data packets.
In yet another aspect of the invention, both RF and IR transmissions may be accommodated by same data and control protocols.
In an additional aspect of the invention, network configuration occurs through an automated, interactive process wherein network node addresses for each network node having a wireless network module are stored in host memory for access in selecting those of the network nodes which will form a network configuration in which wireless messages may be exchanged.